Lookout Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lookout Observatory clear sky chart from 2005-11-06 to 2026-04-02.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	14% 7% 2 6% 5% 4 5% 4 6% 7% 40%	131418
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 43%	130443
Transparency	Day	40% 6% 11% 21% 17% 5%	135180
	Night	38% 5% 11% 22% 19% 6%	134750
Seeing	Day	19% 11% 24% 22% 16% 8%	16475
	Night	17% 9% 22% 29% 19% 4	26568

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	20% 11% 4 5% 3 3 3 2 3 4 42%	5258
	11th to 20th	Day	13% 5% 3 6% 3 2 2 2 3 4 56%	5280
	21st to end	Day	23% 9% 3 6% 3 3 4 3 4 5% 37%	6253
February	1st to 10th	Day	17% 9% 3 6% 4 4 4 4 4 6% 39%	2100
	11th to 20th	Day	23% 8% 2 6% 5% 4 4 3 4 4 37%	2048
	21st to end	Day	21% 7% 2 6% 5% 4 4 3 4 4 40%	1730
March	1st to 10th	Day	19% 8% 3 7% 5% 5% 5% 4 6% 5% 33%	4580
	11th to 20th	Day	13% 7% 2 6% 4 4 3 2 5% 6% 48%	5041
	21st to end	Day	15% 6% 2 7% 5% 4 4 3 5% 7% 42%	5586
April	1st to 10th	Day	13% 7% 2 5% 5% 4 5% 4 6% 7% 43%	2409
	11th to 20th	Day	13% 6% 2 6% 5% 4 4 3 5% 6% 46%	2374
	21st to end	Day	11% 5% 2 6% 5% 4 5% 4 6% 8% 44%	2485
May	1st to 10th	Day	17% 7% 2 6% 5% 4 6% 4 6% 7% 34%	5862
	11th to 20th	Day	19% 7% 3 7% 6% 5% 5% 4 7% 8% 29%	5861
	21st to end	Day	16% 7% 3 6% 4 4 5% 4 6% 7% 39%	6433
June	1st to 10th	Day	11% 7% 2 6% 6% 5% 6% 5% 7% 9% 34%	2600
	11th to 20th	Day	5% 5% 2 6% 6% 5% 6% 6% 9% 11% 39%	2600
	21st to end	Day	7% 5% 2 7% 6% 5% 7% 5% 8% 11% 37%	2600
July	1st to 10th	Day	7% 5% 2 7% 6% 6% 7% 6% 8% 11% 35%	5900
	11th to 20th	Day	7% 5% 2 7% 6% 7% 8% 7% 9% 12% 30%	5900
	21st to end	Day	11% 9% 3 9% 8% 7% 7% 6% 8% 11% 21%	6424
August	1st to 10th	Day	6% 3 2 4 5% 5% 6% 5% 9% 11% 44%	4112
	11th to 20th	Day	7% 4 2 6% 5% 5% 6% 6% 9% 11% 39%	3849
	21st to end	Day	9% 4 2 5% 4 5% 5% 4 6% 7% 48%	4312
September	1st to 10th	Day	10% 7% 2 7% 5% 6% 5% 4 7% 9% 37%	2288
	11th to 20th	Day	16% 5% 2 6% 4 5% 5% 3 5% 7% 40%	2200
	21st to end	Day	14% 5% 2 6% 5% 3 4 4 5% 6% 47%	2200
October	1st to 10th	Day	12% 5% 2 5% 4 4 4 3 4 5% 52%	2200
	11th to 20th	Day	10% 5% 2 6% 3 3 3 3 5% 5% 56%	2163
	21st to end	Day	15% 5% 2 4 3 4 3 3 4 5% 53%	2090
November	1st to 10th	Day	13% 6% 2 4 4 3 3 3 4 6% 52%	1852
	11th to 20th	Day	13% 4 2 5% 4 3 4 4 5% 6% 50%	1890
	21st to end	Day	17% 6% 2 5% 4 3 4 3 5% 7% 45%	1890
December	1st to 10th	Day	20% 6% 2 5% 4 4 4 2 4 5% 44%	3020
	11th to 20th	Day	19% 11% 3 8% 4 4 4 3 4 4 38%	3463
	21st to end	Day	20% 7% 3 7% 4 4 4 3 5% 7% 36%	4565
January	1st to 10th	Night	18% 8% 2 7% 4 4 4 3 4 5% 42%	7635
	11th to 20th	Night	14% 7% 3 7% 4 3 3 2 3 4 50%	7680
	21st to end	Night	20% 9% 2 5% 3 4 4 3 4 4 42%	7925
February	1st to 10th	Night	16% 7% 3 6% 4 3 4 3 5% 5% 43%	2520
	11th to 20th	Night	21% 7% 2 8% 4 5% 4 2 4 5% 39%	2458
	21st to end	Night	20% 7% 3 7% 4 4 5% 3 5% 5% 37%	2076
March	1st to 10th	Night	23% 10% 3 7% 5% 4 4 3 5% 6% 31%	5493
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 6% 7% 48%	5138
	21st to end	Night	14% 8% 3 7% 5% 4 4 3 5% 5% 42%	5588
April	1st to 10th	Night	12% 5% 1 4 4 4 4 4 6% 8% 48%	2029
	11th to 20th	Night	13% 5% 2 5% 3 4 3 3 5% 6% 51%	1975
	21st to end	Night	11% 5% 2 5% 4 3 4 4 5% 7% 50%	1915
May	1st to 10th	Night	13% 8% 3 7% 5% 5% 5% 5% 7% 8% 35%	4033
	11th to 20th	Night	20% 8% 3 8% 5% 4 5% 4 6% 8% 29%	4032
	21st to end	Night	13% 6% 2 6% 4 4 4 4 6% 10% 40%	4421
June	1st to 10th	Night	7% 6% 3 7% 5% 6% 5% 5% 7% 10% 40%	1800
	11th to 20th	Night	6% 4 2 5% 4 3 4 4 8% 11% 50%	1800
	21st to end	Night	5% 5% 2 5% 5% 4 5% 5% 8% 12% 45%	1800
July	1st to 10th	Night	6% 5% 2 7% 5% 5% 6% 5% 8% 11% 37%	4058
	11th to 20th	Night	6% 5% 2 6% 5% 5% 5% 5% 9% 13% 39%	4057
	21st to end	Night	10% 8% 3 8% 5% 6% 6% 5% 8% 11% 32%	4427
August	1st to 10th	Night	6% 3 1 4 4 4 5% 4 8% 11% 49%	3033
	11th to 20th	Night	8% 4 2 5% 3 4 4 3 6% 9% 50%	3200
	21st to end	Night	8% 3 2 4 3 3 4 3 6% 8% 56%	3586
September	1st to 10th	Night	9% 6% 3 6% 4 5% 5% 4 7% 9% 43%	2090
	11th to 20th	Night	13% 5% 2 7% 4 4 4 4 6% 9% 43%	2200
	21st to end	Night	12% 5% 1 5% 3 3 4 3 5% 7% 50%	2200
October	1st to 10th	Night	11% 4 2 5% 3 2 3 3 4 5% 58%	2200
	11th to 20th	Night	12% 5% 2 4 4 4 3 2 4 5% 56%	2235
	21st to end	Night	14% 5% 2 5% 4 3 3 3 4 5% 55%	2748
November	1st to 10th	Night	14% 5% 2 4 4 3 3 3 5% 6% 53%	2666
	11th to 20th	Night	13% 6% 1 4 3 3 3 3 5% 6% 53%	2730
	21st to end	Night	15% 7% 2 5% 4 3 4 4 5% 6% 46%	2730
December	1st to 10th	Night	18% 6% 3 6% 3 3 3 3 4 5% 46%	4380
	11th to 20th	Night	18% 10% 3 6% 4 4 3 2 3 5% 42%	4952
	21st to end	Night	21% 6% 3 7% 4 4 4 3 6% 6% 36%	6633

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	47% 3 6% 23% 19% 2	5259
	11th to 20th	Day	33% 3 4 18% 33% 8%	5280
	21st to end	Day	50% 3 6% 18% 17% 7%	6253
February	1st to 10th	Day	45% 4 7% 22% 20% 3	2100
	11th to 20th	Day	50% 3 4 21% 17% 5%	2058
	21st to end	Day	47% 3 6% 17% 20% 6%	1730
March	1st to 10th	Day	50% 4 9% 11% 18% 7%	4580
	11th to 20th	Day	37% 3 6% 19% 22% 13%	5041
	21st to end	Day	42% 4 10% 25% 17% 3	5586
April	1st to 10th	Day	38% 5% 11% 22% 18% 5%	2409
	11th to 20th	Day	39% 4 6% 21% 24% 6%	2374
	21st to end	Day	36% 5% 11% 29% 16% 3	2485
May	1st to 10th	Day	46% 6% 15% 22% 11% 2	5897
	11th to 20th	Day	50% 7% 15% 20% 8%	5865
	21st to end	Day	43% 5% 10% 23% 17% 2	6447
June	1st to 10th	Day	42% 7% 16% 22% 12% 1	2600
	11th to 20th	Day	33% 8% 18% 25% 14% 2	2600
	21st to end	Day	37% 8% 18% 22% 12% 3	2600
July	1st to 10th	Day	36% 11% 19% 22% 10% 1	5835
	11th to 20th	Day	38% 15% 27% 16% 4 1	5831
	21st to end	Day	51% 13% 18% 14% 4	6240
August	1st to 10th	Day	29% 8% 16% 36% 11%	4099
	11th to 20th	Day	33% 9% 17% 26% 13% 2	3885
	21st to end	Day	31% 8% 13% 24% 21% 3	4311
September	1st to 10th	Day	41% 8% 14% 17% 15% 5%	2288
	11th to 20th	Day	42% 6% 11% 22% 17% 2	2200
	21st to end	Day	36% 6% 11% 20% 20% 7%	2200
October	1st to 10th	Day	25% 4 6% 15% 38% 13%	3590
	11th to 20th	Day	21% 2 5% 19% 30% 23%	3507
	21st to end	Day	28% 4 6% 23% 28% 11%	3353
November	1st to 10th	Day	34% 4 6% 19% 29% 8%	1852
	11th to 20th	Day	34% 4 7% 21% 25% 9%	1890
	21st to end	Day	39% 4 6% 21% 25% 5%	1890
December	1st to 10th	Day	43% 3 5% 18% 26% 5%	3020
	11th to 20th	Day	49% 4 6% 19% 18% 5%	3460
	21st to end	Day	46% 4 8% 26% 14% 2	4565
January	1st to 10th	Night	42% 5% 9% 23% 17% 3	7636
	11th to 20th	Night	37% 3 5% 19% 27% 8%	7680
	21st to end	Night	46% 3 4 19% 20% 8%	7925
February	1st to 10th	Night	42% 4 7% 21% 22% 5%	2520
	11th to 20th	Night	49% 4 6% 19% 16% 6%	2459
	21st to end	Night	48% 4 5% 16% 19% 7%	2076
March	1st to 10th	Night	52% 4 7% 15% 19% 4	5493
	11th to 20th	Night	34% 4 7% 19% 22% 14%	5138
	21st to end	Night	44% 4 7% 23% 18% 4	5588
April	1st to 10th	Night	34% 4 12% 22% 22% 6%	2029
	11th to 20th	Night	35% 3 6% 24% 22% 10%	1975
	21st to end	Night	33% 5% 11% 29% 19% 3	1915
May	1st to 10th	Night	45% 6% 16% 20% 12% 1	4060
	11th to 20th	Night	51% 6% 15% 19% 8%	4033
	21st to end	Night	39% 6% 14% 26% 15% 1	4429
June	1st to 10th	Night	38% 6% 17% 23% 15% 2	1800
	11th to 20th	Night	27% 6% 21% 27% 17% 2	1800
	21st to end	Night	30% 7% 20% 24% 15% 5%	1800
July	1st to 10th	Night	35% 11% 20% 24% 8% 1	4015
	11th to 20th	Night	32% 12% 30% 20% 5% 1	4006
	21st to end	Night	44% 11% 22% 18% 4 1	4297
August	1st to 10th	Night	25% 8% 17% 37% 12% 1	3022
	11th to 20th	Night	29% 7% 20% 28% 16% 1	3230
	21st to end	Night	26% 7% 15% 21% 28% 3	3586
September	1st to 10th	Night	37% 7% 17% 19% 15% 5%	2090
	11th to 20th	Night	37% 6% 13% 21% 20% 2	2200
	21st to end	Night	33% 5% 11% 23% 21% 7%	2200
October	1st to 10th	Night	21% 5% 8% 18% 32% 16%	3590
	11th to 20th	Night	19% 2 4 19% 33% 23%	3630
	21st to end	Night	24% 3 5% 25% 30% 12%	4435
November	1st to 10th	Night	33% 4 8% 20% 25% 10%	2666
	11th to 20th	Night	32% 3 5% 22% 28% 10%	2730
	21st to end	Night	39% 4 5% 22% 23% 7%	2730
December	1st to 10th	Night	41% 3 6% 19% 28% 3	4380
	11th to 20th	Night	45% 4 6% 18% 23% 4	4954
	21st to end	Night	46% 4 7% 26% 16% 1	6633

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	32% 22% 32% 12% 1	330
	11th to 20th	Day	35% 20% 31% 10% 3 1	330
	21st to end	Day	27% 26% 33% 12% 2	363
February	1st to 10th	Day	29% 20% 35% 12% 3	330
	11th to 20th	Day	40% 25% 27% 7% 1	330
	21st to end	Day	38% 19% 35% 6% 2	273
March	1st to 10th	Day	32% 19% 33% 13% 3 1	330
	11th to 20th	Day	26% 22% 30% 17% 5% 1	517
	21st to end	Day	21% 17% 38% 18% 6%	594
April	1st to 10th	Day	25% 15% 30% 17% 11% 1	504
	11th to 20th	Day	18% 16% 33% 22% 10% 1	492
	21st to end	Day	17% 13% 33% 20% 13% 3	500
May	1st to 10th	Day	17% 15% 29% 23% 11% 5%	503
	11th to 20th	Day	17% 8% 24% 29% 13% 10%	527
	21st to end	Day	16% 7% 19% 26% 21% 12%	573
June	1st to 10th	Day	16% 5% 20% 29% 17% 13%	530
	11th to 20th	Day	7% 5% 16% 30% 24% 19%	530
	21st to end	Day	10% 4 18% 28% 24% 17%	530
July	1st to 10th	Day	11% 3 10% 27% 29% 19%	525
	11th to 20th	Day	9% 3 10% 23% 32% 22%	524
	21st to end	Day	8% 3 9% 27% 31% 22%	576
August	1st to 10th	Day	15% 3 11% 24% 28% 19%	526
	11th to 20th	Day	13% 3 12% 32% 27% 14%	519
	21st to end	Day	15% 5% 9% 26% 30% 15%	583
September	1st to 10th	Day	10% 4 15% 31% 28% 12%	530
	11th to 20th	Day	17% 4 13% 24% 31% 10%	530
	21st to end	Day	16% 6% 17% 29% 26% 6%	530
October	1st to 10th	Day	15% 5% 23% 28% 22% 7%	530
	11th to 20th	Day	14% 10% 27% 30% 17% 2	530
	21st to end	Day	20% 11% 27% 26% 14% 2	473
November	1st to 10th	Day	22% 14% 31% 23% 8% 2	330
	11th to 20th	Day	17% 18% 40% 21% 4	330
	21st to end	Day	20% 22% 33% 18% 5% 2	330
December	1st to 10th	Day	31% 19% 37% 10% 2 1	330
	11th to 20th	Day	27% 20% 31% 17% 5%	330
	21st to end	Day	31% 16% 35% 14% 4 1	363
January	1st to 10th	Night	25% 16% 31% 23% 4	840
	11th to 20th	Night	22% 18% 30% 24% 6%	840
	21st to end	Night	22% 16% 37% 22% 3	924
February	1st to 10th	Night	20% 15% 33% 29% 3	840
	11th to 20th	Night	26% 20% 31% 22% 2	823
	21st to end	Night	27% 17% 33% 21% 3	692
March	1st to 10th	Night	20% 16% 30% 29% 5%	840
	11th to 20th	Night	20% 15% 31% 26% 8% 1	840
	21st to end	Night	19% 14% 30% 27% 10%	924
April	1st to 10th	Night	15% 16% 27% 31% 11% 1	622
	11th to 20th	Night	15% 11% 31% 30% 12% 2	593
	21st to end	Night	13% 9% 24% 37% 17% 1	600
May	1st to 10th	Night	11% 7% 27% 32% 21% 2	600
	11th to 20th	Night	14% 6% 19% 34% 20% 6%	591
	21st to end	Night	13% 3 12% 32% 35% 4	650
June	1st to 10th	Night	9% 3 12% 37% 34% 6%	600
	11th to 20th	Night	7% 1 12% 33% 37% 12%	600
	21st to end	Night	7% 2 9% 30% 43% 10%	600
July	1st to 10th	Night	9% 3 7% 25% 42% 15%	585
	11th to 20th	Night	8% 2 6% 23% 46% 15%	582
	21st to end	Night	9% 2 7% 25% 46% 10%	657
August	1st to 10th	Night	9% 2 6% 25% 45% 13%	597
	11th to 20th	Night	13% 4 8% 28% 39% 9%	594
	21st to end	Night	14% 4 7% 27% 40% 8%	660
September	1st to 10th	Night	10% 3 11% 32% 36% 9%	690
	11th to 20th	Night	16% 3 10% 29% 38% 5%	800
	21st to end	Night	14% 4 15% 30% 34% 4	800
October	1st to 10th	Night	12% 5% 20% 33% 25% 5%	800
	11th to 20th	Night	15% 7% 23% 34% 19% 2	800
	21st to end	Night	16% 8% 22% 36% 16% 3	880
November	1st to 10th	Night	17% 8% 22% 33% 17% 2	820
	11th to 20th	Night	16% 11% 30% 31% 11% 1	840
	21st to end	Night	21% 11% 26% 30% 11% 1	840
December	1st to 10th	Night	25% 13% 27% 28% 6%	840
	11th to 20th	Night	23% 12% 28% 28% 8%	840
	21st to end	Night	27% 13% 25% 29% 6%	924

Page generated at 2026-03-30 01:18:43. Version ac07

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